Electrical shield



April 7, 1936. G. n. M LAREN ELECTRICAL SHIELD Filed April 16, 1954 FIGURE 12' F/GURE I f/vvz/vroe -ATTORNEY8 GEORGE [/2 WIN l7AcL ARE/V Patented Apr. 7, 1936 UNITED STATES PATENT OFFIE ELECTRICAL SHIELD sylvania Application April 16,

2 Claims.

My invention relates to electrical shields for radio apparatus. In apparatus employing thermionic tubes, it is generally necessary or desirable to shield parts of the circuits and thermionic tubes to avoid undesirable reactions between the various elements.

It has previously been the practice to shield thermionic tubes by metallic shields. Such shields may be drawn or fabricated from sheet metal. The shield covers the thermionic tube and fastens to a base fitting. The connection between the base fitting and the shield may be a forced fit or a bayonet lock type. In any event the grounding of the shield depends upon the fit. Too tight a fit, may result in a bent or broken shield; too loose a fit, gives imperfect grounding and rattling of the metal parts from vibration. Such vibration is present in portable sets and sets where the loudspeaker is mounted on or near the base.

I propose to overcome these difiiculties by an improved method of shielding which will eliminate the base fitting. My invention will also result in savings of material and labor over the previous types of tube shields.

Figure I shows a sectional view of one form of my shield enclosing a thermionic tube.

Figure II illustrates one method of fabricat ing the tube shields of my invention.

In Figure I, I represents a base member on which is suitably fastened a thermionic tube socket 2. Through a hole 3, the thermionic tube 4 is inserted in the socket 2. Surrounding tube 4 is shield 5. The shield 5 is composed of three laminations. Laminations 6 and l are of flexible insulating material; such as, paper stock of about .010 inch thickness. Lamination 8 is a thin metal foil. I have found copper foil of .001 inch thickness suitable, but tin, aluminum or other metal may be used. The inner lamination 8 may be a spiral wrapped paper tube sirnilar to mailing tubes. The laminations 6, and 8 are preferably straight wraps or layers. The reason for this preference is the improved appearance of a straight layer as well as the simplicity of handling the very thin foil layer, which for convenience may be first fastened to the heavier wrapper S. The various laminations are glued together.

The top of the tube shield may be rolled as illustrated at 9. The roll improves the appearance and may be of sufiicient extent to bear against the tube 4 to steady the shield 5. However, the rolled edge 9 is not essential. The straight edge of Figure II may be employed.

1934, Serial No. 720,918

In either case, the tube shield may bear on the glass envelope of tube 4 to support and locate the shield.

The metal foil 8 should be grounded to make effective the electrical shielding. A simple ter minal may be made by driving a metallic staple i0 through the complete shield 5 and tightly clinching the ends H and i2. A wire l3 may be soldered to the staple Ill. The length of the wire may be sufiicient to permit removal of the shield without disconnecting the end 14 which is usually grounded to the base.

In Figure II, I have shown one method of fabrication in which sections of the laminations have been turned back for illustration purposes. 5 represents the complete shield assembly. I represents the inner lamination which may be one or more layers of spirally wrapped paper. The metallic foil layer may be seen as 8. The outer layer 6 is shown as a straight wrap with its beginning and end at line IS. The terminal connection already described may be employed or other suitable connections may be substituted.

Although I have shown three laminations, as my preferred construction, it is possible to use two laminations; i. e., one of foil and one of paper. Likewise, although I prefer metallic foil, sprayed metallic coating may be substituted. The outer layer may be suitably painted for best appearance.

The tube shield I have described is just as eifective electrically as a solid metal shield. It is cheap to manufacture and will not give a metallic rattle which often results from vibrations in the solid metal shields. Further, the shield of my invention does not require a base fitting. The flexibility of my construction makes it easy to install and eliminates the dangers of bending usually present in the sheet metal type of shield.

I claim:

1. A device for shielding a thermionic tube w comprising, a layer of insulating material of cy-.

GEORGE IRWIN MACLAREN. 

